Social networking systems enable users to interact with various objects represented within the social network. For example, a social networking system allows users to designate other users or entities as connections (or otherwise connect to, or form relationships with, other users or entities), contribute and interact with their connections, post media or commentary, share links to external content, use applications, join groups, list and confirm attendance at events, invite connections, and perform other tasks that facilitate social interaction. External applications also use the services of a social networking system to allow authenticated users to incorporate some of the above social interactions with use of the external applications. Similar interactions may also be a part of the user experience within other network services.
Sharing a link (e.g., a Uniform Resource Locator (URL), Uniform Resource Identifier (URI), or other address or reference to a source of data, collectively referred to herein as a “link” or “hyperlink”) as a post within a social network enables users to select or otherwise activate the link (e.g., by copying and pasting the link into a browser application). Doing so causes the user's processing device (e.g., via the browser application) to render the linked content. A user viewing the link alone, however, may not want to follow the link without some indication of the underlying content. As a result, a social networking system may generate a preview including one or more of an image, title, and summary data from the linked content. For example, the social networking system uses a scraping algorithm to extract the preview content from the linked resource and publish the preview content along with the link.
Requests to share the same linked content may be received in great numbers. In the interest of conserving processing resources, the social networking system caches or otherwise stores a copy of the preview content for reuse. Linked content, however, may change over time. As a result, the preview content may no longer accurately represent the linked content. Additionally, different sources of linked content change at different rates.